The role of hepatitis B virus (HBV) in human cancer is being investigated by (1) transfection analysis of HBV and HBV genes into human cells and (2) nucleic acid hybridization analysis of peripheral blood lymphocytes (PBL) and lymph node tissues from various HBV-risk group patients. Since there is no in vitro system for HBV infection of human cells in culture, the application of viral transfection analysis provides the only available method to study the virus in vitro. HBV core (HBc) gene transfection into mucoepiidermoid carcinoma cells (NCI-H292) and hepatocellular carcinoma cells (Malove) provides a model system to study the regulation and expression of a cytopathologic viral gene. Although the surface antigen gene (HBs) is constitutively expressed, the HBc gene is regulated by methylation of a HpaII site 276 base pairs from the AUG-start site of the HBc structural gene. The hormonal and nutritional requirements regulating the expression of the HBc gene are being studied. Although viable normal human hepatocyte cultures have been difficult to obtain, we are initiating experiments to transfect HBV into adult hepatocyte cultures for transient assays of viral gene products and studies of viral cytopathology associated with its role in liver carcinogenesis. Screening of nucleic acids from HBV risk group patients' PBL and lymph node tissues indicates the following: (1) HBV sequences, transcripts, and replicative DNA can be detected in serologically negative HBV patients' tissues; (2) approximately three of five chronically infected (CAH) patients' PBL nucleic acids contain viral transcripts and four CAH patients' PBL DNA samples contained replicative forms of HBV on Southern hybridization; (3) the slot-blot testing of larger groups of patients will provide information relevant to disease status that may be more sensitive than serologic evalution since serologically negative patients can be screened for HBV-nucleic acid sequences. In addition, the mode of DNA replication may be determined from HBV DNA isolated from PBLs and lymph nodes